In the summer of 1916 William Butler Yeats asked Maud Gonne to marry him. This had become something of a habit over the twenty-seven years since he had first met and fallen in love with her and, as he put it, "the troubling of my life began." From then on he had devoted a considerable part of that life to Maud Gonne and to the idea of Maud Gonne, writing poems and plays inspired by her and by her incomplete refusal of him, trying to rescue her from the mind-boggling series of personal catastrophes that made up her life, communing with her astrally, and even, eventually (a fact that should cheer the hearts of unrequited lovers everywhere), sleeping with her, in Paris, in 1908, "the long years of fidelity," as another of his lovers commented, "rewarded at last." But as Yeats himself said, "the tragedy of sexual intercourse is the perpetual virginity of the soul." By 1916 Yeats was over fifty and wanted to be married and to produce an heir. He knew that Maud, for all the beauty he had once seen in her, or thought he'd seen in her (in photographs she looks like a towering, lantern-jawed man), had gone too far down the road of rabid revolutionary political activism, chloroform addiction, and increasingly Christian mysticism to be anything like a suitable wife. So when he made his request this time, it was really only because he thought he should, because her estranged husband, John MacBride—a drunken gunman, the father of her son, and the molester of her daughter—had recently been executed by the British for his role in the 1916 Easter Rising. Yeats made his proposal in a perfunctory fashion, with conditions attached, expecting and somewhat hoping to be turned down yet again, as he was. As R. F. Foster writes in this much anticipated second and final volume of his biography of the great Irish poet, occultist, and sucker for romantic punishment, "When he duly asked Maud to marry him, and was duly refused, his thoughts shifted with surprising speed to her daughter."

The sad life of Iseult Gonne is one of the many peripheral stories that Foster expertly sketches in the margins (though she deserves, if that's the word for it, a biography of her own). Twenty-one that summer, Iseult was Maud's second child with Lucien Millevoye, a married French anarchist and newspaperman; she had been conceived in the mausoleum of her short-lived brother, in an attempt to reincarnate the dead infant. She had been presented to the world as her mother's adopted niece; had been molested by her stepfather at the age of eleven; had, for her own part, proposed marriage to Yeats when she was fifteen; and now was widely considered a great beauty (a judgment borne out by photographs), although she, like her mother, was something of a giantess. Iseult would go on to be seduced by Ezra Pound, with whom Yeats unwisely secured her a secretarial position; to work with her mother as a gunrunner for the IRA; and to marry the impossibly bad Irish novelist Francis Stuart, a sadist and nincompoop who would eventually leave her, in 1940, to emigrate into Nazi Germany.

In that year of many proposals Iseult, like her mother, turned Yeats down. Determined to marry someone, he asked George Hyde-Lees, a twenty-four-year-old woman whom he knew through occult circles. He was accepted (despite the remark made by one of her cousins: "George ... you can't. He must be dead"), was married, and then on their honeymoon found himself down with a bad case of buyer's remorse—feverish, exhausted, and listless with regret. At this point George began to write automatically, taking dictation from celestial "instructors" who appeared like a kick line from the wings to save her marriage even as they provided her husband with the basis for A Vision, his endlessly revised mystical opus. Barely a year later Yeats would find himself turning away Maud Gonne (who was disguised as a Red Cross nurse to escape detection by the British authorities) from her own house in Dublin, where he was living with his pregnant bride.

If you think that all this sounds like something out of Ponchielli's La Gioconda, or CBS's Guiding Light, you're not alone. The novelist James McCourt once wrote that Yeats, a figure of unmatched imperiousness, "seems to have gone from the inner sanctum of the Order of the Golden Dawn to the board room of the Abbey to Thoor Ballylee to the halls of high deliberation without once having stepped in shit." There's some truth to that. But Foster shows, in this learned and engaging biography, that Yeats's life, however elevated the realms in which it unfolded, was nothing if not messy. Most of the saga related above is contained in the first hundred pages or so of Foster's book—and matters hardly get more sedate or conventional as the story goes on.

Even Yeats's public life was operatic in its incident and intensity of emotions. The Arch-Poet begins just at the lead-up to the Easter Rising, the initially unpopular insurrection in Dublin that, though doomed itself, led in surprisingly short order to the partial and then the complete independence from Great Britain of twenty-six counties of Ireland. Yeats was in England during the Rising, which was staged by a small, fanatical offshoot of the Irish Republican Brotherhood—a group he had been involved with in the 1890s. Since then he had shifted toward what is sometimes called, in discussions of the dizzying variety of Irish political positions, constitutional nationalism, as opposed to physical-force nationalism. Yeats wanted an independent Ireland, but he thought that this could be better achieved by pursuing parliamentary action and undertaking nationalist cultural projects—his Abbey Theatre, for instance—than by exploding administrative buildings and murdering policemen. The latter method, however, won out. Foster adeptly charts Yeats's, and Ireland's, changing responses to the "martyrs." This group included a number of people whom Yeats knew personally, notably John MacBride—a man who had once threatened to shoot him ("the only cheerful piece of news I have had in days," Yeats said at the time; "it gives one a sense of heightened life"). His transformation into an elegist of the martyrs in such poems as "Easter, 1916," "Sixteen Dead Men," and "The Rose Tree" thus has a particular strangeness.

Foster is a historian rather than a literary scholar, and his disentangling of the complicated skein of Irish political and revolutionary activity over the broad period under consideration is one of the book's great strengths. But it is the fantasia of Yeats's personal life, rather than his various performances as a public man, that is most compelling. Toward the end of the biography is an extended episode, straight out of Evelyn Waugh at his cruelest, in which the elderly Yeats, having traveled to Majorca with Shri Purohit Swami (a flatulent Hindu mystic with whom he was "translating" the Upanishads) and Lady Gwyneth Foden (a deranged and vindictive fraud whose real name was Gertrude Woolcott), is stricken with nephritis and has to be rescued by his stalwart wife from his suddenly hostile companions, and also from the help offered by his crazed paramour, Margot Ruddock, an aspiring actress. This all transpired shortly after Yeats had had a vasectomy in an attempt to restore his sexual potency. ("Who am I," he once asked a friend, "that I should not make a fool of myself?") George Yeats, who comes across as an extraordinary woman in many ways, said to him around this time, "When you are dead people will talk about your love affairs, but I shall say nothing, for I will remember how proud you were."

Be that as it may, the Yeats of his latter years, in the throes of what he called his "second puberty," can be hard to like. What we often see, if we put aside his writing, is an impotent, blue-haired eugenicist enmeshed with a series of unlikely women; preoccupied by notions of heredity, of blood and soil; but nomadically rootless and largely disengaged from his wife and children. Even Thoor Ballylee, his emblematic stone tower, was abandoned once he'd used it up as a subject for poetry. Much has been made of Yeats's supposed flirtation with fascism, and Foster is especially good at delineating his swervings in this direction; but in truth Yeats's political ideas, to the degree to which they can be discerned at all, are more akin to the aristophilic sub-Nietzschean philosophy of the German writer and soldier Ernst Jünger, only less coherent. Like the invisible celestial instructors, they were there to bring him metaphors for poetry.

And so there remains the poetry, the writing that justifies the biography —"the great unwieldy poem, all light and mud," as Daniel Albright, the editor of the finest edition of Yeats's Poems (Everyman), once described the Cantos of Ezra Pound, Yeats's erstwhile disciple. Yeats's poems are certainly more polished and individuated and approachable than the Cantos, Pound's long, fragmentary, famously impenetrable masterpiece/aesthetic junk heap. Still, Albright's phrase seems equally apposite to his body of work. There's no doubt that Yeats's writing contains a large amount of mental clutter and mystification, which alters in nature but does not diminish as his career proceeds. But amid the home-brewed, Matrix-like transcendentalism and the relentless armorial emblemology —lions and gyres, celestial unicorns and misspelled figures from Celtic mythology—is a constant incursion of what the writer Patrick Kavanagh called "Homeric utterances, poetry sweeping through." And there at the end is "The Circus Animals' Desertion," an astonishing thing, a piece of deathbed self-excoriation so convincing that it's hard not to agree with Yeats that all his previous poems were weak and misguided—hard, that is, until one revisits passages like this, from the great war poem "Nineteen Hundred and Nineteen":

But is there any comfort to be found?
Man is in love and loves what vanishes,
What more is there to say?

What more is there to say, indeed? If Yeats started his writing life enamored of a notion of disembodied spiritual elitism, at the end, steeped in "the fury and the mire of human veins," trying to begin again in "the foul rag-and-bone shop of the heart," he seems closer to Shakespeare's Edmund at the moment of his last, desperate cry, "I pant for life." And that's where Yeats leaves us, breathing and dying. The spit and blood are wet upon the page.